1. Field of Invention
The present invention relates to systems, methods and apparatuses for explosively breaching and destroying munitions, for example conventional munitions that are normally encountered in military EOD field clearing operations or chemical munitions, which are contained in an overpacked shipping or storage container that is preferably housed in a sealed detonation chamber.
2. Description of Related Art
Note that the following discussion refers to a number of publications by author(s) and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-à-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
Various techniques currently use explosives to rupture military ordnance. Most techniques use a counter charge consisting of a block of demolition explosive placed in direct contact with the piece of live ordnance. Other techniques employ shaped charges that are placed directly on top of the munition, thus penetrating the munition and igniting or detonating the high explosive filler contained within the ordnance. Though these techniques have proven to be very effective, they are ineffective in destroying a munition such as a chemical munition that is housed in a steel overpacked shipping container and is to be de-milled in a total containment detonation chamber. Overpacked munitions are typically leaking or damaged munitions, which are typically placed in metal tubes with special seals to prevent further leakage.
When destroying ordnance with a demolition block of explosive that is in direct contact with the munition, the charge detonates and delivers a high intensity (approximately 150-300 kilo bars) shock pulse inside the munition. This high intensity shock pulse travels through the wall of the ordnance shell and into the shell's high explosive filler. The intensity of the direct shock coupling diminishes as it travels through the wall of the projectile and into the explosive. Depending upon both the intensity and duration of the shock pulse, and the sensitivity of the explosive filler, the projectile's explosive filler can be ignited, deflagrated, or detonated.
Techniques using shaped charges usually deploy a copper lined conical shaped charge that produces a hypervelocity copper projectile that penetrates the munition and either deflagrates or detonates the munition's explosive filler. Other techniques employ the use of wedge-shaped metal lined linear shaped charges that cut into the munition's casing and ignite or deflagrate the explosive filler.
While both of these described techniques are effective for destroying bare conventional munitions in an open environment, these techniques are an ineffective means of safely destroying, for example, a chemical-filled projectile contained within a shipping/storage overpacked container which is being de-milled/destroyed within a total containment detonation chamber.
The overpacked container or housing presents a problem that renders the above techniques useless in a controlled and completely contained environment. The desired effect is to breach the munition and destroy the chemical filler without causing harm to the sealed containment chamber. Due to the standoff distance (distance between munition/projectile's surface and position of the counter charge) created by the wall of the overpacked container, contact charges cannot effectively deliver or communicate their energy to the projectile's surface, and thus the shock intensity from the contact counter charge is greatly reduced. The intensity diminishes approximately as the inverse square to the inverse cube of the distance from the charge's surface. Thus the barrier created by the overpacked container typically renders the contact charge technique useless to breach projectiles contained in an overpacked container.
The distance provided by the overpacked wall also creates a problem of using conventional wedge shaped linear-shaped charges to breach thick-walled chemical-filled projectiles. A commercial linear-shaped charge has a void typically shaped into a chevron or inverted “V” along its entire length, thus employing a wedged-shaped or chevron-shaped geometry. A linear-shaped charge is designed to cut linearly through its target. Standard linear-shaped charge liner angles range from 80-100 degrees.
FIG. 1 is an illustration of a standard linear-shaped charge comprising high density high explosive filler 2 enveloped in metal housing 3 with chevron-shaped or wedge-shaped metal liner 4 at the base of the charge. The charge is typically initiated at one end, and the detonation traverses down the axis of the charge at the velocity of the detonating explosive.
Upon detonation, explosive filler 2 exerts extreme pressures into metal housing 3 and metal liner 4. The pressures begin to accelerate the liner material 4 from each side towards the axis of the charge.
The pressures induced into the liner segments are so large (greater than 200 kilobars) that the strength of the liner may be neglected and the liner material may be treated as a non-viscous fluid that behaves hydrodynamically. In other words, upon detonation, the explosive generates high intensity shocks that induce high pressures into the liner wall of the shaped charge. The pressure generated is far beyond the elastic-plastic limit of the metal, thus accelerating the metal liner in a fluid-like manner onto the axis of the charge. These charges collapse the wedge or chevron shaped liner producing a high velocity fluid-like stretching metallic jet. Due to the impact pressure of the metallic jet on a target surface, both the jet/target interfaces behave hydrodynamically.
The jets are capable of penetrating steel and other hardened targets. The penetration capability of a metallic jet formed by a shaped charge is a function of the effective jet length. To a first approximation, penetration into hardened targets, such as steel, is proportional to the length of a coherent jet whose velocity along its entire length (jet tip to tail) is sufficient to cause plastic flow of the target during impact.
As the two sides of the liner material collapse symmetrically and impinge upon each other, the metal begins to flow inward and collide at anterior collision point A. This collision point A is aligned with the bisector of the interior angle of the liner adjacent to the charge axis. Under these extreme pressures, the metal liner flows from the collision point in two opposite directions along the axis of the charge. Simultaneously, the liner material flowing toward the apex of the charge forms slug 5 while the liner material flowing away from the charge apex forms jet 6.
Though traveling in opposite directions, both the slug 5 and the jet 6 have equal velocities within the flowing liner mass. Since the liner mass is accelerated away from the expanding explosive products, the entire liner mass (both jet and slug) has a net forward velocity in the direction of the jet. Segments of the liner mass are accelerated by the adjacent explosive mass. Changes in the quantity of adjacent explosive mass cause the liner mass segments to accelerate at varying rates. These changes in acceleration yield varied pressures of impact as segments of the liner mass impinge upon each other at collision point A. This variance in impact pressures creates a blade-shaped projectile that exhibits a substantial velocity gradient along its length. The projectile velocity decreases monotonically from jet tip 7 to tail 8. The liner material near the liner's apex region is adjacent to the greatest quantity of explosives. This produces the highest velocity during impingement which forms the front forward end of the jet or jet tip 7.
Typical linear wedge-shaped geometries produce jets with tip speeds ranging from 10,000 ft./sec. to 15,000 ft./sec. while the rear of the jet travels at approximately 3,000 ft/sec. Due to this large velocity gradient, the jet stretches very quickly with distance; i.e. the jet stretches as the standoff distances increases. With wedge or chevron type linear-shaped charges, the jet has stretched to its maximum length after traveling approximately two charge diameters. Within this short distance the jet begins to stretch and then breaks apart. At this point, the jet begins to break apart into pieces 9 resulting in a decrease in penetration or cutting capability.
Therefore, common 90° angle linear-shaped charges producing jets with high velocity gradients dissipate quickly over long standoff distances making them unsuitable for penetrating steel-type or hardened targets at long standoff distances. Thus the conventional linear-shaped charge is an ineffective tool to cut/penetrate steel-type targets at long standoff distances.
The present invention comprises a method of deploying shaped charges that are effective at penetrating targets at long standoff distances.